<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #d1{
            width: 100px;
            height: 100px;
            border: 10px solid red;
            /*圆角:值越大越圆,超过宽高一半时为正圆(前提是正方形)*/
            border-radius: 100px;
        }
        #d2{
            width: 100px;
            height: 100px;
            border: 1px solid red;
            /*内边距会影响元素的宽高*/
            padding-left: 50px;

        }
</style>
</head>
<body>
<ul>
    <li>aaa</li>
    <li>bbb</li>
    <li>ccc</li>
</ul>
<div id="d2">内边距</div>
<div id="d1"></div>
</body>
</html>